Compact disks (CDs) are formed by an optically transparent plastic, such as a polycarbonate, like General Electric's Lexan, which is an easily molded plastic material capable of transmitting a light beam, such as a thin laser beam, without scattering, refracting or distorting the light beam. CDs are generally manufactured in a 120 mm format, although an 80 mm "single" format is available. With such 120 mm CDs, approximately 74 minutes of a digital signal, which is generally either music or an audio presentation, may be stored in the outer circumferential portion of one side of the disk having a radial extent of approximately 58.5 mm. In the production of such CDs, the trademarks and alphanumeric information identifying the disk content are normally silk-screened onto the side of the CD opposite the side to be read by the laser of the CD player.
The manufacture of CDs begins with a glass plate which has one surface highly polished to provide a smooth flat surface which is cleaned to be free of dirt. A photoresistive material is applied to the polished and clean surface of the glass plate to form a uniform thin film with a constant thickness which can only vary about .+-.50 angstroms. After the photoresistive coating on the surface of the glass plate has been cured and inspected, the digital data representing music or visual images is formed in the photoresistive coating by modulation of a high energy laser beam. The photoresistive material is then developed in the pattern of the digital data and the photoresistive material forming the pattern of the digital data is removed from the glass plate, leaving a photoresistive coating on the surface of the glass including a pattern of "pits" which represent the digital data and the music or audio information. A silver coating is formed over the photoresistive coating with its pattern of pits representing the digital data, preferably by sputtering, to provide a "master" for use in the formation of CDs. The master is then electroplated with nickel at a variable plating rate to provide a mating form for molds to replicate the digital data by injection molding. This mating form is referred to as a "stamper", and/or the "master stamper" and/or the "father stamper".
Rather than use this form in production tooling, the father stamper is replicated to provide the production molds actually used in the production of CDs. In a manner known in the art, the nickel stamper is oxidized using an oxidizing agent. After oxidation, the oxidized nickel stamper is washed with water and isopropyl alcohol and is placed into a plating bath to be plated with nickel to build a negative image in the form of the original master, referred to as a "mother" disk. The nickel mother disk is stripped from its father stamper and oxidized with an oxidizing agent and washed with water and isopropyl alcohol. The resulting mother is used to form production stampers for use in injection molding of the CDs by the same process described above in the production of the father stamper from the master.
The production stampers provide a mold surface to form the digital signal pits in the polycarbonate CDs formed by injection molding. That is, polycarbonate plastic material is injection molded against the production stampers and, when removed from the injection molding machine, provides a CD substrate including on one surface pits in the pattern of the digital data representing the recorded music or audio information. The surface of the polycarbonate CD with the recorded information is then coated with a reflective aluminum coating by sputtering and after inspection, the aluminum-coated recorded surface on the recorded side of the CD is protected by a coating of lacquer, or other such protective coating.
After the lacquer coating is cured, desired indicia are silk-screened onto the lacquer coating in a manner well known in the art. Such indicia frequently include the trademarks of the record company, the name of the performer, the names of the recorded songs, the number and running time of the various tracks and other such information.
In reproducing the recorded information on the CD, the CD player directs a laser beam through the polycarbonate material forming the uncoated side of the disk and senses the variations in reflection of the laser beam from the pits and the reflective aluminum coating to reproduce the recorded music and audio information and the like.